This invention relates to a wiper link mechanism oscillating a wiper blade which wipes off raindrops, dust and the like existing, for example, on a surface of a front windshield of an automobile, and especially, relates to a sealing structure of a ball joint for a wiper link mechanism which connects a link arm with a link connecting rod of the wiper link mechanism.
A ball joint having a normally used structure for an automobile is assembled to, for example, a steering shaft, a propeller shaft, a drive shaft and the like. A ball joint of this type for an automobile has a relatively large length in the direction of the axis and lip-parts of the sealing member for the ball joint do not easily cause interference with other parts or members.
On the contrary, in case of the ball joint for a wiper link mechanism, the space between the plate-shaped link arm and the plate-shaped link connected rod is very narrow, whereby the lip-parts of the sealing member adopted between the link arm and the link connecting rod easily cause interference with other parts or members.
Therefore, it is necessary to introduce a peculiar sealing structure for the ball joint of the wiper link mechanism.
A prior art sealing structure for a ball joint for a wiper link mechanism, for example, is shown in FIG. 6.
A ball joint 101 shown in FIG. 6 is composed of a ball pin 103 and a ball retainer 106. The ball pin 103 is fixed to a link arm 102. The ball retainer 106 connected to a link connecting rod 104 is provided with a spherical hollow 105 for forming a spherical pair with said ball pin 103.
The ball pin 103 is inserted into said spherical hollow 105 of said ball retainer 106 through an opening 107 provided at the lower part of said spherical hollow 105 in FIG. 6, whereby said ball pin 103 coupled with said ball retainer 106 performs a free power-transmission.
A boot 112 which is formed from an elastic body is inserted between the under surface of the ball retainer 106 and upper surface of the link arm 102 in FIG. 6.
In the ball joint 101 having the above mentioned structure, said boot 112 prevents the penetrating of water, mud or the like into the spherical hollow 105 from the lower part of said ball retainer 106.
However, in the above mentioned ball joint 101, it is very rare to transmit the power at the state in which the link arm 102 and the link connecting rod 104 are kept in parallel to each other as shown in FIG. 7. Generally, the power is transmitted at the state in which the link arm 112 or the link connected rod 104 is tilted. When the link arm 102 or the link connecting rod 104 transmits the power in an inclined position, the boot 112 cannot be deformed in response to the movement of said link arm 102 and the link connecting rod 104. Therefore, sometimes a space is formed between the ball retainer 106 and the boot 112 or between the link arm 102 and the boot 112, and then, water, mud and the like may enter into the spherical hollow 105 of the ball retainer 106 through said space.
This causes a problem in that the ball pin 103 and the spherical hollow 105 of the ball retainer 106 wear away remarkably. Thereby the life of the ball joint 101 is reduced and smooth movement of the ball joint 101 is prevented. On the other hand, it is a possible problem that the ball pin 103 pops out of the ball retainer 106.